Metal fibril compacts



April 7, 1970 A. LuKscH ETAL 3,505038 METAL FIBRIL COMPACTS Filed Aug.24, 1964 13 Sheets-Sheet 1 By Brera. 151/0034526- Jrmwfys April 7, 1970A. LuKscH ETAL 3,505,038

METAL FIBRIL COMPACTS Filed Aug. 24, 1964 13 Sheets-Sheet 2 /NvNToRs F IE'.. E /A/mms 108541/ BY Bear/z. J." .Sm/P3224 Afro/wars April 7, 1970 ALUKSCH ETAL 3,505,038

' METAL FIBRIL COMPACTS Filed Aug. 24, 1984 15 shees-sneet 8 By 3812774JS Sun/pasa? April 7, 1970 A. LuKscH l-:TAL

METAL FIBRIL COMPACTS 13 Sheets-Sheet 4 Filed Aug. 24, 1964 a/tzmrrakmsxs April 7, 1970 A. LuKscH ETAL 3,505,038

METAL FIBRIL COMPACTS Filed Aug. 24V, 1964 13 Sheets-Sheet 5 INVENTOP s4410x545 404/547/ 311581271.: 15214108826 MW gm April 7, 1970 A, LUKSCHEl' AL METAL FIBRIL COMPACTS Filed Aug. 24, 1964 FIE. E

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13 Sheets-Sheet 8 SOURCE INVENTORS 441222845 zxsc/l BY .EZ-'R774 .Z' S(In/085194 April 7, 1970 A, LuKscH ErAL METAL FIBRIL coMPAcTs 13Sheets-Sheet 9 Filed Aug. 24, 1964 4 ;Z mkp z WWW Wsv VI 4 w w 48,

April 7, 1970 A. LuKscH ETAL METAL FIBRIL COMPAC'I'S Filed Aug. 24, 196413 Sheets-Sheet 10 April 7, 1970 A. LuKscH ETAL METAL FIBRIL COMPACTS 13Sheets-Sheet 12 Filed Aug. 24, 1964 April 7, 1970 A, LUKSCH ETAL3,505,038

METAL FIBRIL COMPACTS Filed Aug. 24, 1964 13 Sheets-Sheet 13 BY Baz 7/4.I 504108526 MW Wvwm United States Patent O U.S. Cl. 29-1835 15 ClaimsABSTRACT OF THE DISCLOSURE Method and product: Compacts composed offibrils of tough, recalcitrant metals such asV stainless steel; thedensity of the compacts being about 30% to 85% of the density of themetal of which the '*fibrils are composed. The fibrils range intransverse dimension from about .0005 toV .005 inch, have an area lessthan that of a .002 inch circle, are of uniform length, and are made byshearing off narrow width pieces from the end of a rolled strip ofparent metal. Individual fibrils have the two flat rolled faces of theparent strip and two sheared faces, the width of one of the shearedfaces being wider than the other as a result of shearing, so that thecross section of the fibril ranges from roughly triangular to squashedfour-sided configuration with the two rolled faces converging toward thenarrower of the sheared faces. Compacts are made by separating thefibrils and air lifting them against a traveling screen through whichloose extraneous burrs, chips and slivers are substantially removed,thereby leaving a mat of fibrils substantially free from degradedparticles which might otherwise contaminate the matY and migrate throughit. The mat has excellent green strength and is compressed throughseveral stages preferably with intermediate annealing until the densitesare obtained. Compacts of varying densites throughout the thickness ofthe compact may be prepared. The compacts composed of the compressed mat(or layers of mat) may be supported on exterior surfaces by Woven orreticulated metal support members. Extremely recalcitrant metals such ashard-to-work Type 347 stainless steel alloy and similar diflicultlymachinable metals may be utilized for making the original fibrils. Thefinished compacts are useful for sophisticated filtering and the likeapplications and for transpiration cooled surfaces.

The present invention relates to metal fibril compacts and to methodsand machines for making such compacts.

The metal fibril compacts of the present invention are formed from novelmetal fibrils which, if desired, may be made from metals having thehighest available factors of mechanical strength and toughness andtemperature and corrosion resistance. The compacts of the presentinvention may thus have, in turn, factors of mechanical strength andtoughness and temperature and corrosion resistance far exceeding anyfibrous-metal devices previously available.

It is an object of the invention to provide such fibrousmetal devices.

The invention provides fibril compacts having the qualities of improvedmechanical strength, toughness, a wide range of pore sizes, Controlleduniformity of pore size, graded pore size (when desired) a wide range ofdensites, very high temperature and corrosion resistance, improvedfreedom from degenerate particles and hence from particle migration,freedom from deterioration, and what is very important, lowered costs.It is an object of the invention to provide fibrous metal devices havingthe aforesaid advantages.

The present invention provides novel methods and machines forfabricating mats from a bulk quantity of novel loose metal fibrilswherein, in such methods, and the starting material, which is alreadysubstantially free from slivers, chips, burrs and the like degeneratesmall particles, is maintained clean as by re-cleaning and is thenfurther processed in such a manner for mat formation that un-attachedslivers, chips, and the like degenerate material will not be formed toany great eXtent during mat formation or if formed, will besubstantially removed. The result is that small and unwanted particlesare for practical purposes eliminated from the mat and from the finalfibrous compact made therefrom, and uses of the complete compacts forsophisticated `duties will not be impaired.

One of the features of the invention is the formation of a 'web or matof metal fibrils having good green strength such that it may be handledwithout deterioration during processing for maintaining uniform densitythroughout the mat during processing and in the ultimate finishedproduct.

The green strength of the compact is of much importance in producingcommercially useful items inasmuch as the Originally formed mat mustremain homogeneous at least during the early stages of formation inorder that the finished product shall reliably provide a uniform (orControlled) density and pore size. The importance of green strength willbe appreciated when it is realized that the webs or mats of theinvention, when first made, may have a density in the range of about 1%or 2% and in the finished product may have a density from 15% to 20% upto %-80% or even more.

It is an object of the invention to provide methods for making lowdensity metal fibril mats under close conditions of control and handlinghaving the aforesaid characteristics and to provide such mats.

It is another object of the invention to provide improved tubular andflat-formed fibrous metal compacts useful as filters, transpirationdevices, fuel burners, structural members, and the like.

Other and further objects are those inherent in the invention hereinillustrated, described and claimed and will be apparent as thedescription proceeds.

To the accomplishment of the foregoing and related ends, this inventionthen comprises the features hereinafter fully described and particularlypointed out in the claims, the following description setting forth indetail certain illustrative embodiments of the invention, these beingindicative, however, of but a few of the various ways in which theprincples of the invention may be employed.

The invention is illustrated by the drawing's wherein the same numeralsrefer to the same parts and in which:

FIG. 1 is a photograph enlarged twelve times showing the metal fibrilsused as the starting material for making the compacts of the presentinvention;

FIG. 2'is a photograph enlarged eighty times showing several of thefibrils used as the starting material for making metal fibril compactsof the present invention and showing the details of the edge,configuration of these fibrils. 'In this photograph a drawn wire ofknown dimension is shown for purposes of comparison;

FIG. 3 is a photograph enlarged twelve times showing the fibrils used asthe starting material for making the metal fibril compacts of thepresent invention. In this photograph the fibrils are shown in a loosepile. This photograph illustrates the various twistng and turning of thefibrils, the intertwining thereof, and the many varieties ofintersections and type of contact between the fibrils;

'FIG. 4 is a part schematic longitudinal sectional view i of one form ofa machine used for carrying out the process for forming the fibrilsillustrated in FIGS. l, 2 and 3 into a loose vmat of substantiallyuniform density 3 and configuraton as a first stage of making a metalfibril compact according to the present invention;

FIGS. 5, 6 and 7 are very much enlarged fragmentary perspective views,partly in section illustrating various types of contacts which developbetween the fibrils when they are compacted into mat formation. FIG. 5shows an edge-to-edge (point) contact; FIG. 6 shows an edge-toedge(line) contact and FIG. 7 shows a face-to-face (area) contact;

FIG. 8 is an actual size photograph of a short piece of a length of aloosely formed mat composed of fibrils of the kind shown in FIGS. 1-3after the fibrils have been processed by the machine shown schematicallyin FIG. 4;

'FIG. 9 is an actual size photograph showing a short piece of a lengthof the mat of 'FIG. 8 after it has been initially compressed by rollingit to improve its green strength, and showing the details of fibrilorientation and intersections as this greater density;

FIG. 10 is an actual size photograph of a short piece of a length of themat of FIG. 9 after it has been annealed in an annealing furnace andtrimmed to width;

FIG. 11 shows two views at A and B. View A is a plan view and view B isa side (edge) view of a strip of metal fol from which the fibrils ofFIGS. 1-3 have been made. In view B, the thickness of the strip isgreatly enlarged;

FIG. 12 is a side elevational view of the mat of FIG. 8;

FIG. 13 is a side elevational view of the mat of 'FIG. 9;

FIG. 14 is a side elevational view of the mat of FIG. 10;

The three views, FIGS. 12, 13 and 14 show for comparison the thicknessof the lfibril mat when just formed, (FIGS. 8 and 12) initialcompression (FIGS. 9 and 13) and after annealing (FIGS. 10 and 14).

FIG. 14A is a schematic side view illustrating a way for initiallycompressing the mat shown in 'FIG. 14 by rolling it to increase itsdensity;

FIG. 15 is a perspective view of the mat of FIG. 14 showing it attachedto a preformed inner filter screen and illustrating the first step offormation of the mat of FIG. '14 into a tubular filter for fluids andthe like;

FIG. 16 is a front elevational view of a machine of the inventionutilized for spirally winding the component of FIG. 15 into a tubularform on the preformed inner filter screen;

FIG. 17 is a side elevational view of the device of FIG. 16;

FIG. 18 is a fragmentary enlarged vertical sectional view taken alongthe line and in the direction of arrows 18-18 of 'FIG. 16 illustratingan early stage of the spiral winding process by which the component ofFIG. 15 is formed into tubular configuration;

FIG. 19 corresponds to FIG. 18 and shows the final stages of the samespiral winding process;

FIG. 20 is a fragmentary much enlarged portion of the vertical sectionalview of FIG. 18 and illustrates the arcs of contact between the pressurerollers and the mat (of FIGS. 14 and 15) during an early stage of thespiral winding of the component of FIG. 15 as it is wound into a tubularconfiguration;

FIG. 21 corresponds to FIG. 20 and shows the increased areas of contactbetween the mat and the pressure rollers during the final stages ofwinding of the mat (of FIGS. 14 and 15) into a tubular configuration;

'FIG. 22 is a front elevational view of a machine which may optionallybe utilized in a subsequent step a method of the invention for insertingthe spirally wound-up mat inner screen component into an outermechanical support screen;

FIG. 23 is a sectional view taken as on the line and in the direction ofarrows 23-23 in FIG. 22;

FIG. 24 is similar to FIG. 23 and is a fragmentary enlarged Verticalsectional view of the device of FIG. 22 taken at substantially rightangles to the view of FIG. 23, illustrating the machine with thewound-up inner screen and mat assembly positioned within an outermechanical support screen;

FIG. 25 is a horizontal sectional view taken as on the line and in thedirection of arrows 25-25 in FIG. 24;

FIG. 26 is a schematic representation of various process Steps of amethod of the invention for formation of tubular filters and fiatfilters;

FIG. 27 is a longitudinal sectional view of the completed tubularconfiguration filter comprising an inner perforated member, la metalfibril compact filter media, and outer mechanical support perforatedmember and with finishing end caps in place on the filters;

FIG. 28 is a schematic representation of the steps of another method ofthe invention for compacting a mat, such as that lshown in FIG. 14 intoa dense fibrous metal component which can, for example, be used as intranspiration cooling device or for other uses; and

FIG. 29 is a schematic representation of another method of theinvention, illustrating the single step compression of a low densityfibril supply, 'such 'shown at the left in FIG. 26, for forming a highdensity finished component.

Throughout the drawings corresponding numerals refer to the same partsor elements.

Referring now to the drawings the discussion will deal first with theunique fibril metal starting materials which, according to thisinvention, are used for the construction of fibrous meal compacts ofmany descriptions. The fibril metal starting materials and the machinesand methods for their production are the subject of an application ofBertil J. Sundberg, Ser. No. 391,707, filed Aug. 24, 1964, executed Aug.21, 1964 and entitled Metal Product and Method and Machine for MakingSame, to which reference is made for a full delineation of the fibrilmetal starting materials used herein. For completeness however, suchunique starting materials are described herein, as follows:

FIBRIL METAL STARTING MATERIA The basic component of the fibril metalcompacts forming the product of this invention is, of course, thefibrils themselves. -FIG. 1 is a photograph magnified twelve timesshowing representative metal fibrils used in the 'preferred embodimentof the invention. From FIG. 1 it can be seen that these fibrils areelongated in respect to their cross 'sectional dimensions; they have aslight twist throughout their length. The light and dark spots on thefibrils show this twist. It can also =be seen that the fibrils areuniform in lengh and are of substantially uniform cross section.

Although for the purposes of photography the individual fibrils 49 shownin FIGS. 1, 2 and 3 were held between glass slips and thereby physicallymaintained in a common focal plane, the fibrils 49 when released willhave a springness and due to their slight bends, they will, whenrandomly oriented in a bulk supply, display a good 'but not excessiveamount of "loft. That is to say, la pile of the fibrils will standresiliently, without packing and with 'little development of parallelismbetween adjacent fibrils. Individually, the fibrils are resilient, theyhave some but not excessive, bends.

The fibrils shown in FIGS. 1, 2 and 3 are made from Type 347 stainlesssteel, and are illustrative of the extremely tough and recalcitrantfibril starting materials which may be nilized pursuant this invention.By the terms tough and recalcitrant is meant materials which cannotreadily be machined with ordinary cutting tools. Before theaforementioned invention of Bertil J. Sundberg, it was ne'ver possibleto make at any economical cost, a metal wool of, for example Type 347stainless steel. There just was no economical way to make wool from Type347 stainless steel.

We do not mean to imply that Type 347 sta-inless steel is the only toughmaterial that may 'be utilized pursuant this invention. There are manyother tough metals and alloys and the selection will therefore dependupon the characteristics desired, i.e. density, corrosion resistance,heat resistance, heat and electrical conductivity, abrasion resistance,etc.

The present invention is also applicable when, a fibril startingmaterial is used which has the configuration and other characteristicsof that herein described for the tough, recalcitrant metal 'fibrilmaterials but is composed of more easily machinable metals (i.e.ordinary 'steel and its alloys, non-ferrous metals), but in such event,'some of the cost yadvantages as compared to other 'available methodswill be lost. However, many advantages of the invention such as freedomfrom 'substantial amounts of detached burrs, slivers, chips anddegradation particles, good loft, unifor-mity in respect to port sizeland distribution '(and hence uniformity of density of the finishedproducts) pore shape, convenience of manufacture, etc. are stillretained.

In some instances homogeneous mixtures constituting the fibril startingmaterial may be used. Examples of these include but are not limited tofibril mixtures of -ferrous 'and non-ferrous materials, or fibrils madefrom coated metals or bi-metals, homogeneou-s m-ixtures of metallic andnon-metallic fibrils.

Pursuant the aforesaid application of Bertil J. Sundberg, the originalmaterial is rolled to a very thin strip and is cut into strips, then thefibrils are severed as very thin strips of rolled strip by a successionof short shearlike tool blows of extremely short time-dur'ation but ofimmense energy, one fibril being severed from across the end of thestrip for each such shear-'like tool blow. The fi-brils so made are ofuniform length and of hair-like dimensions. They have facescorresponding to the 'rolled faces of the strip 'and fractured faces.The fibrils are of small cross-section, usually much less than thecross-section of a .002 inch wire. As made, they are 'slightly tomoderately bent along their length 'and they have a slight to moderatetwist. They have a tensil strength which, as nearly as can 'bedetermined, approximates that of the parent material. A 'bulk supply ofsuch fibrils is substantially free from detached burrs, chips, Slivers.and degraded particles, but will (when viewed under the microscope)exhibit some roughness and an occasional attached 'burr and exhibitsroughness on the fractu-red faces of the fibril and along the edges ofsuch face. The crosssecitonal shape of the fibrils of one batch mayinclude some which are like a -squashed rect'angle having two opposedangul-arly disposed nearly 'straight boundaries (apparentlycorresponding to the rolled faces of the strip from which the fibril wassevered), said faces being connected by an inwardly roughly cu'rvedminor length boundary and an outwardly curved major length boundary(apparently corresponding to the fractured faces of sever'ance). In somein'stances the minor length inwardly cu'rved 'boundary will nearlydisappear, in which event the cross-section approaches a triangularshape. Reference is made to the aforesaid application of Bertil J.Sund'berg for additional microphotographs and description of the fibrilstarting material.

FIG. 2 is a photograph of the fibrils enlarged eighty times. It can herebe seen that the fibrils 49 have two smooth faces and two sheared orsevered faces. The smooth faces apparently correspond to the oppositerolled faces of the foil strip from which the fibrils are cut and thesevered faces apparently are those resulting when the fibrils aresevered from the ends of the strip. In the photograph of FIG. 2 the curland twist of the individual fibrils is clearly evident and the abovedescribed physical characteristics of the fibrils can be seen. Note thatthe severed faces appear rather irregular and rough on the faces andalong the edges. The rough edges on the fibrils are believed to actanalogously to the scaly surface of naturalwool fibers and are'believedto be responsible for the i favorably high green strength of compactsmade from the fibrils. Also, these surface and edge irregularities arebelieved to assist in trapping dirt and other small particles when adensified compact is used as a filter.

,These same surface and edge irregularities are believed to improve thebond 'between the fibrils when they are compressed into compacts, and toassist in making firm attachment when the compressed compacts are`brazed or 6 sintered. The increase in surface area due to the surfaceand edge irregularities are also useful in extending any phenomenarequiring a solid-fluid interface, as where a compact composed of suchfibrils is used as or for holding a catalytic element in chemicalreactions.

For size comparison FIG. 2 includes a .001 inch round wire. This isshown at 30 in FIG. 2.

FIG. 2 also illustrates some of the types of contacts which occurbetween fibrils when they are in contact with each other. At 31 thereappears to be a substantially flat face-to-face contact while at 32there appears to be an edge-to-edge contact. It will -be noted that thefibrils are substantially free from slivers, burrs, chips and detachedparticles of degradation.

When the fibrils are placed into a loose pile and pressed between glassslips, as shown in FIG. 3, they will intertwine, cross, and interconnectin the widest variety of ways. When released from pressure the mass willalways be three-dimensional inasmuch as the fibrils have good loft, theyare springy (prior to annealing) and are irregularly oriented andproject in every direction. The random orientation of the fibrils isclearly evident in this photograph, FIG. 3.

For most purposes, and as an example of smaller size fibrils used inthis invention the fibrils may be very fine, nearly hair-like. Forexample they may have a cross section Wherein one transverse measurementthrough the section is .0015 inch and another measurement through thecross lsection may be, say .0009 inch or even less, for example down to.0005 inch. The length of such fibrils might be 3A inch. The crosssectional dimensions of the fibrils can, of course, be increased as canthe length. Usually the largest cross sectional transverse dimensionswill be under .005 inch on down to say .0009 inch and even lower, say.0005 inch. The length will usually be about 0.5 inch to about 1.5 inch,but longer or shorteri lengths can be used. Fibrils of such dimensionalparameters give good results in this invention.

METHODS IN GENERAL A supply of fibril starting material of the aforesaidkinds and characteristics, having been obtained, it is then processedthrough a plurality of -steps which are carried out with appropriatemachines, several of which are used. The invention provides severalmethods and a variety of machines. Different machines may be used andsome may not be needed, depending upon the particular final productdesired.

In general the methods of this invention comprise compacting the fibrilstarting material, which in bulk may ha-ve a density of 1% or less ofthe solid material of which the fibrils are composed, until the densityis increased to that desired in the final article, which may be as lowa's for example 5% to 8% up to as high as, for example, 75 Thecompaction is accomplished in a nonliquid environment, preferably butnot necessarily in several steps and preferably lbut not necessarilywith one or more intermediate annealings. There are many advantagesinherent when the working environment is non-liquid, not the least ofwhich is low cost and freedom from involvement of the fibril materialwith anything foreign to the ultimately desired finished article. Byusing successive steps in compacting the fibrils it is possible tointroduce layering as a parameter and this helps to avoid channeling andpermits variable density objectives to be easily obtained; hencemultiple step compaction is preferred. By using intermediate steps ofannealing (between successive compactions) the material, even though ofthe toughest metals, can usually be brought to high, even extreme,densities and intermediate annealing is preferred.

It is a feature of the invention that the bulk fibril startng material,being initially clean and substantially free from detached burrs,slivers, chips and degraded particles, is maintained clean during thevulnerable phases of subsequent processing. This is accomplished byintroducing separated fibrils into an upwardly moving stream of highvelocity clean air by which they are transported by the air stream andinto contact with a preferably downwardly facing reticulated web,against which they build up and form a mat which is a low densitycomposite of high-Velocity impinged, interlaced, randomly disposedfibrils. The mat, even though of the very lowest density at this stage(around 1% density as compared to an equal volume of the material ofwhich the fibrils are composed) will have a strength sufficient toretain its integrity and it will cling to the under-side of the web ofits formation meanwhile being substantially cleaned of any unattachedparticles of degradation (burrs, chips, slivers, etc.) or maintainedclean by the through-passage of the high velocity airstream used in itsformation. The fibrils can of course be combed out to disintegrate themat and, preferably this is done once more and the mat reformed byupward or downward high Velocity airstream.

In either way, using a one stage or a two stage matformation willprovide a usable very low density fibrilcomposed homogeneous matsubstantially free from separate particles of degradation, havingsufficient strength (i.e. green strength) for subsequent handling and ofuniform density throughout. Two stages of mat-formation are preferred.

Then, depending upon the ultimate article being produced, the mat may,in appropriate sized pieces be laid in layers and compressed or it maybe rolled up as a cylinder and compressed, either with or without one ormore steps of intermediate annealing. Also, the compressive pressuresmay be increased for successive layers, or in successive stages` The mat.may be compressed against a woven screen of the same or anothermaterial (as the fibril material) and compressed.

In a final stage the composite is subjected to temperature sufficient toweld the fibrils where they are in contact, (or at least increase thebond between them) or, if a brazing ingredient fibril has been included,to braze them together. Where the final compaction is against a wovenscreen, attachment will be attained between the compacted fibrils andthe screen, due to the final heating at elevated temperature.

METHOD OF FORMING MATS OF FIBERS One illustrative embodiment of amachine for forming mats from the fibril starting material, isillustrated schematically in FIG. 4. FIG. 4 is actually a schematicrepresentation of a machine made by Curalator Corporation, EastRochester, N.R., their Model No. 18 BS. Since FIG. 4 is schematic itshould be considered only as illustrative of the kind of machines usedin carrying out a process of the invention. The particular elements canbe varied to meet the varying circumstances. The machine includes anouter housing-frame generally designated 50 which forms a hopper andserves as a frame for various components of the machine and supplies themechanical structure. Housing 50 has a hopper portion 51 with a largehopper loading opening 52 at one end thereof.

The hopper 51 has a bottom movable conveyor belt 53 mounted on suitableend rollers 54, 54. One roller can be driven through any suitableadjustable speed drive, in the direction indicated by arrow 55 to movethe bulk supply 62 of metal fibrils slowly toward the rear part of thehopper so that the pile of fibrils will engage the upwardly moving frontrun 60 of conveyor 56. The conveyor 56 is mounted on a pair of spacedapart vertically spaced rollers 57, 57 which are rotatably mounted onthe frame 50 and driven through suitable adjustable speed drivemechanism (not shown). The conveyor 56 which has outwardly extendingneedle-like teeth 61, and as the front run 60 move upwardly, the teeth61 disengage fibrils from the adjacent face of the pile 62 of fibrils,and transport. the fibrils upwardly as indicated by arrow 63.

At the upper end of the upright or vertical conveyor 56 the fibrilscarried by teeth 61 are engaged by teeth 64 on an upper horizontalconveyor assembly generally designated 65. The teeth are mounted on abelt 66 which is mounted on suitable rollers 70, 70 which in turn aredriven by an adjustable speed mechanism (not illustrated). The rollers70 are rotated in the direction of arrow 71 so that the teeth 64 moveoppositely to the direction of travel of teeth 61 on conveyor 57. Thusteeth 64 comb down and level out the fiow of fibrils as they aretransported upwardly by conveyor 57 and in so doing help to maintain auniform flow of fibrils illustrated at 72, as the fibrils are carriedover the top of the upright conveyor 56.

In the center section of the machine, illustrated generally at 75, thehousing 50 is formed into an elongated tunnel-like throat of decreasingcross-section toward the right of FIG. 4. In this throat are placed apair of spacedapart rollers 76, 76 which are rotatably mounted. Therollers serve to mount a reticular endless belt 77 which is mounted soas to run on the rollers. The belt 77 is driven so that its lower passmoves to the right as shown by arrow 73 when the rollers 76, 76 arerotated in a conventional manner by suitable adjustable speed powermechanism (not shown).

As shown in FIG. 4, the wall 80 of the center section 75 of the machinehas a large rectangular rear air-Outlet 81 cut therethrough. The port 81opens into the interior of the center section 75 and between the upperand lower runs of belt 77. A suitable duet 82 is connected to the port81 and also to the intake side 83 of a suction blower 84 which is driventhrough a suitable motor 85.

The suction blower 84 is of a high capacity and evacuates air from thetubular center section 75 of the machine. Most of the air will enterthrough opening 52 of hopper 50 and then pass around through inlet end86 into section 75.

It can be seen that the opposite (right) end of the center section 75 issubstantially blocked off from entrance of air by a nest of rollers at91, and by the right end roller 76 and belt 75. Sealing strips 87, 87extend down from the top of center section 75 and almost to thoseportions of belt 77 where the belt passes over rollers 76, 76. By theseexpedients the opportunity for air to by-pass the path of fiow throughthe lower run of belt 77 is decreased.

Air will therefore fiow into hopper 50, thence through opening 86. Atopening 86 the flow is via arrow A1 down through the space between theback (right in FIG. 4) side of upper roller 57 and the adjacent roller76, as shown by arrow A4, and in so doing the air flow assists indislodging from needles 61 on conveyor 57 the flow of fibrils that havethereby been separated from bulk supply 62. The airflow A2-A4 is strong,and turning upwardly and to the right (FIG. 4) carries the hair-likefibrils along with it and as the airflow passes through the lower run ofbelt 77, as at arrows A3 and A4, the fibrils are intercepted by thenet-like belt, while the air passes through the belt, and into opening81 at arrow A5 thence via arrows A6 and A7 through blower 84 and arethen exhausted at A8. Un-attached degradation vparticles (burrs, chips,slivers, dirt, extraneous material) if any, are carried along with theair and are hence removed from the fibril mat, which is meanwhile builtup on belt 77 and held there by the airflow.

The lower pass of belt 77, moving to the right, arrow 73, carries thefibril mat to a place 95 where a plurality of small rollers indicatedgenerally at 91 very gently compact the mat and support the mat -untilit engages a stripping roller 92 which is powered to rotate in directionas indicated by arrow 93.

The roller 92 engages that side of the mat which has been towards belt77 and gently guides the mat under roller 92 and along floor to andunder feed roller 94.

The mat of fibrils will thus be mpelled by the rollers 92 and 94 outover the end of floor 90 Where it emerges. The rollers 92 and 94 arerotated under power by suitable means (not shown) in a substantiallycylindrical chamber 95 which houses a high speed breaker roller 96.Roller 96 is what is called a lickerin roll. The lickerin roll 96 isrotated in the direction indicated by arrow 97 as at extremely highspeeds by a suitable drive (not shown). The outer peripheral surface ofthe lickerin roll 96 is provided with a plurality of forwardly directedsicklelike sharp pointed teeth 100. These teeth, moving rapidly acrossthe approaching end of the mat, tear the metal fibrils loose, separatingthem loose from the mat and thus loosened fibrils are projected asindividual fibrils onto a venturi chute 101 leading from the chamber 95.Below and slightly to the left of the lickerin roll 96, as shown in PIG.4, there is provided a roller 107B which is rotated in the direction ofthe arrow shown thereon (clockwise). This roller closes against theadjacent lip 107Atof the air duct 107 and the proximate upper edge 101Aof the lower wall 101B of venturi duet 101. The upper portion of theroller 107B (which is the portion clockwise from lip 107A to edge 101B)acts as a closure from the lip to the edge and it is between suchsurface of roller 107B and the proximate surface of the lickerin rollthat the very high Velocity air flow and the dislodged fibril will fiow.

The venturi chute 101 is expanded in direction away from the lickerinroll. At the bottom end of chute 101 there is rotatably mounted acondenser roll 103 which is made of a reticulated metal or woven wirecloth, and is driven by an adjustable' speed drive in a clockwisedirection as shown by arrow 103A. The condenser roll 103 is rotatablymounted in a housing and the center of the condenser roll is evacuatedwith a vacuum blower 104, drawing through the surface of roll 103operating through a conduit or duct 105 which communicates with astationary duet 105A in the interior of the condenser roll. The roll 103is mounted so that it rotates with respect to the interior duct 105 andair is drawn through the chute 101 and through the condenser roll 103.The vacuum blower 104 pulls the air through internal duct 105A thencethrough duct 105, blower 104 and the air is then either discharged or,after 'being filtered, it may be recirculated to duct 107 which conveysthe air up to the space between lip 107A and the underside of fioor 90.Thence an extremely high Velocity of air is projected at arrow A9towards and against the lickerin roll 96 and thefiow of individualfibrils lossened thereby. The fiow impells the separated hair-like metalfibrils downwardly through the duct 101 and against the exposed outerarcuate portion of reticulated roller 103 where the fibrils areintercepted and a mat built on the reticular surface of roll 103. Thefibrils are diposed at random and in every conceivable orientation anddue to their high Velocity impact, are more tightly formed as a mat thanon belt 77. The air passes through roller 103 and duct 105A to berecirculated or can be discharged and fresher drawn in.

This air fiow carries the individual metal fibrils downwardly with ahigh Velocity against the surface of the condenser roll and theimpingement of the fibrils accordingly builds up a mat surface offibrils which is interlaced and has good green strength.

The individual metal fibrils, which are thus intercepted by and retainedon the outside of the condenser roll 103, are formed into a fiuifyhomogeneous mat 110. The mat 110 is removed from the condenser roll asthe condenser roll rotates. It should be noted that the condenser roll103 is mounted on a suitable shaft and driven from suitable adjustablespeed power means (not shown), A stripper roll 112 which rotatesclockwise as shown by the arrow thereon, is provided for lifting the soformed mat 110 from the condenser roll 103 for delivering it to theloading end of the conveyor belt assembly 113 which is provided formoving the mat away from the machine. Conveyor belt assembly 113 can beany standard conveyor belt mounted on a pair of rollers 114, 114 and isdriven by any suitable adjustable speed drive, not shown so as to carrythe mat away at the same speed as it is formed.

Since the individual metal fibrils are separated by the lickerin rolland carried at high Velocity in an air stream and projected against thecondenser roll the resultant orientation of the fibrils is completelyrandom and the fibrils in the mat thus generated are completely randomlyoriented, intertwined and interlocked. The fibrils are not physicallyattached together but the edge and surface roughness of the fibrils,when so formed into a mat cause the fibrils to resist separation, andthe mat, even though having a density of only 1% to 1.5 of the densityof the metal of which the fibrils are composed, has exceptional greenstrength. The mat is light, lofty and of uniform density throughout.

The airflow passing through the mat as it is formed is at high Velocityand any particles of degradation, 1.e. burrs, chips, slivers extraneousdirt, etc., which are not actually attached to a fibril, will be drawnthrough the net-like surface of condenser roll 103 and hence removedfrom the mat. Hence the fibrils are actually vacuum cleaned twice, bythe airfiow A4 through the 'mat formed on belt 77 in the center section75 again by the airflow at A12 through the mat as it is being formed oncondenser roll 103. To insure cleanliness it is best, in most factorylocations to filter incoming air supplied to the system, as at 107FN.

CHARACTER OF THE FIBRIL MAT FORMED The mat which is formed by theprocess of this invention, as on the machine shown in FIG. 4, is an evenstrip of uniform thickness composed of fibrils uniformly distributed.The fibrils are laid and intersect each other in every conceivabledirection. Three common modes of intersection are shown in FIGS. 5, 6and 7 (as well as FIGS. 2 and 3). In these figures, the fibrils 49 whichare made as previously described are shown as having a substantiallyedge-to-edge (or point-type) contact at 116 in FIG. 5; a substantiallysurface-to-edge (line-type) contact at 117 in PIG. 6 and a substantiallyface-to-face (area type) contact as at 118 in FIG. 7.

The edge-to-edge and edge-to-face contacts, particularly where roughnessoccurs provides excellent adherence between the contacting fibrils. Thefiibrils cling together and resist separation. This is believed to -bedue, at least partially, to the roughness which causes the fibrils tohold together in much the same way as woll fibers hold together.Whatever may be the reasons, the resultant mat has sufficient greenstrentgh so that it is capable of being handled in various stages ofsubsequent processing, without disturbing the random orientation of theindividual fibrils or disturbing the condition of uniform density of themat from section to section in the mat.

The mat 110 coming from the machine (FIG. 4) has uniform density in alldirections of about 1% to about 11/2 During the subsequent compressionand annealing of the mat the condition of uniformity of density (whichis also to say, the uniformity of distribution and size of the Voids)will not change. Even though the mat may be enormously reduced in volumeand its density increased the condition of uniformity of density anduniformity of distribution and size of the voids, will not change. Thisuniformity property of the products of the invention is a valued featureof the invention. Just why it occurs is not fully understood but it isbelieved to be due to a condition of uniformity of the starting material(length, cross-section, degree of bend, degree of twist, springiness,loft) plus the exceeding almost hair-like fineness of the fibrilstarting material, plus uniformity in the gentle handle of the tinyfibrils in laying up the mat. In any event, the mat 110, even though ofvery low density, is of great uniformity, and absent subsequent roughhandling, will preserve its uniformity (and all attributes flowingtherefrom) when it is later on reduced to smaller and smaller thickness.

FIG. 8 is a fully size photograph of the top of a portion of a mat 110made accordaning to a process of the invention and on the machineillustrated in FIG. 4. It can be seen that the individual metal fibrils49 are oriented in every direction, curled together, and make everyconceivable type of contact with each other. The mat is very porous, andhas, in fact, a density of approximately 1% to 2%. For the purposes ofthis specification, density is defined as the weight of a unit volume ofthe mat (or compact) divided by the weight of the same volume of a solidmetal of the same material as that used to make the fibers. Thus, wherea given mass or volume of the mat or compact is said to be 2% density,it means that this volume of mat weighs 2% as much as an equal volume ofthe solid metal from which the fibrils are made. Porosity is 100 minusthe density. Thus, a mat having a "density of 2% has a porosity of (100%minus 2%) i.e. 98%.

Therefore, it can be seen that the mat coming from the machine is of lowdensity, hence extremely porous; it is flulfy, and would easily tend toseparate except for its eX- cellent green strength which is believed tobe due to the curling and twisting together of fibrils and theinterlocking and intertwining of these fibrils so that the moderatelyrough edges of contacting fibrils will catch each other and engage togive to the mat the attribute of increased green strength.

A side view of the mat 110 shown in FIG. 8 is illustrated in FIG. 12.The mat has a good Vertical heght and the metal fibrils are uniformlydisbursed and extend in all directions, transversely, longitudinally andvertically, and it is springy.

MAKING USABLE COMPACTS In order to make a usable metal fibril compact,the flulfy, springy mat 110 is further processed. The first optionalstep in this further processing is an initial compression of the mat 110into a mat substantially one-half as thick. This initially compressedmat 120 is shown in FIG. 9, which is also a top view. FIG. 13 is theside view. To accomplish the initial compression the mat 110 is carriedon a strip of paper P. At this stage, the mat is tender, and the paperadds support for handling. As the mat is received from the machine (FIG.4) it is simply rolled with a suitable roller so as to apply relativelylow pressure to reduce the thickness of the mat about one-half andthereby provide a mat having a density of approximately two to fourpercent. This mat 120, FIGS. 9 and 13, has a density of two to fourpercent; it has an improved green strength as compared to the mat 110received from the machine, FIGURE 4. Some of the metal fibrils in themat appear to be bent beyond the yield point so as to take a permanentset. The contacts between individual fibrils are also strengthened andthe fibrils are more firmly pressed into mating engagement with otherfibrils with the various manners of contact shown in FIGURES -7. So thepressure is applied to the mat, even though gentle pressure, the fibriledges, being minute, will, it is believed, generate fairly large unitpressures, with the result that the edges of fibrils bite into otherfibrils. The rough edges shown in FIG. 2 also give good adherencebetween contiguous fibrils. When supported on paper strip P, the mat canwithout deterioration, be rolled and unrolled for transport, storage andfurther handling. If two mat layers are placed against each otherwithout being separated by paper they will adhere and cannot thercaftereasily be separated.

The mat 120, after it has been rolled as shown, is then preferablypassed into an annealing furnace where it is annealed at a temperatureof substantially 2000 F. in a reducing atmosphere (hydrogen). Annealingcauses the mat to settle, even without pressure being applied. Afterannealed, the mat appears as in the photograph FIG. 10 and may be placedupon a strip of paper for handling and storage. The side edges S S ofthe mat have been trimmed. This annealed mat, designated 121, is shownin side view in FIG. 14. During the annealing operation the internalstresses of the metal fibrils are relieved, and the mat sags down simplydue to its own weight. In other words, the density of the mat againsomewhat increases (increase from about 1.5 to 2 times previous value),or in this instance to about four percent to about six percent. The matstructure at this stage appears to be more dense, as can be seen in FIG.10 and the metal fibrils are still in a random pattern with thedifferent interconnecting edge surfaces and the overlapping andintertwining of the fibrils giving a very substantial amount of greenstrength in all three dimensions. At this stage the mat can be stored,handled, shipped and processed without deterioration.

Thus the mat 110 coming off the machine, FIGURE 4, can immediately becompressed to the condition at 120, FIGURES 9 and 13, and t-hisprelimnary rolling is recommended, especially where the very low densitymat 110 must be transported or perhaps stored before being annealed, tocondition 121, FIGURES 10-14. After annealing the mat is very strong,before annealing it is, by comparison, somewhat weak, but stilladequate. However if the conveyor belt 113-114 (FIGURE 4) isappropriately arranged, the mat 110 can be passed directly to theannealing step and and the pre-compression step (pre-rolling) may thenbe eliminated.

The annealed mat 121 is then ready to be processed in further stepswhich will vary in accordance with the desired end product being made.Two examples of what products can be made from, the compacts or mats ofthe invention, are more fully described herein. The final range ofdensity will be from about 15 percent to percent or even more, dependingon the usage. Preferred ranges of density are specified in the examples,the first of which is now described.

CONSTRUCTION OF TUBULAR FILTER MEDIA This example relates to a highpressure fiuid filter for filtration of highly corrosive materials andother sophisticated uses requiring great strength and freedom fromcorrosion such as is provided by Type 347 stainless steel and the likematerials. For these uses it has previously been the practice to providefilters made of very fine mesh woven wire screen. Very finely woven wirescreening is expensive, of limited supply, and when used in a highlycorrosive application or applications requiring great strength andreliability such as filtration of aircraft hydraulic oil, the finescreen has had to be made out of non-corrosive, high strength materialsuch as Type 347 stainless steel. To get a fine screen requires a finewire. Hence fine stainless steel wires woven together to make a screenbecomes prohibitively expensive and can only be used where cost is noobject. It has been found that moderate density metallic compacts madeaccording to the present invention are of such uniformity that they canbe used for such sophisticated filtering Operations. The filters so madeare of low enough price so as to make them a throw-away item. Thedensity range and thickness of the compacts can be varied to providevariations in filtering efi'iciency, etc.

According to one embodiment of the invention there is still provided atleast one layer of filtering woven wire screen final barrier forparticles, but the filters of this invention are primarily pressureconsolidated compacts of fibrils. The tubular inner screens use muchless of the expensive filter screen material than the standard pleatedscreen design. Thus in an exemplary embodiment a length of annealedmetal fibril mat is spirally wrapped tightly around an inner cylinder ofwoven wire screening of proper mesh to form a tube which is then furtherconsolidated with pressure and then sintered into a compact body. Themetal fibril compact actually performs the major work of filtration, theinner screen being mainly a factor of safety. For greater density in thefinal filter, the mat 121 may be prerolled after annealing, as shown inFIG. 14A. The mat is passed through a pair of rollers 119, 119 that areresiliently rigged together, much like a Washing machine wringer. Therollers can be power driven in a suitable manner or can be hand cranked.A further major reduction in thickness can be achieved this way.

FIG. 15 illustrates a cut-length of uniform width mat after it has beenannealed, and if desired further compressed as shown in FIG. 14A. Theout-length is designated 123 and it is of any length to provide one orseveral turns when wrapped on itself to form a tube. As shown, one edgeof the strip 123 is lightly tacked by spotwelding it onto an innertubular support 122 composed of woven wire screening. The strip 123 ofannealed fibril compact material is left to hang free and is suspendedfrom the inner screen 122. The inner screen and also the fibril compactare made of stainless steel, for example Type 347 stainless. The screen122 is made of finely wolven stainless steel wire of required mesh whichis selected according to the particular use of the filter. The screen isrelatively light in weight and does not possess much structuralstrength. Further, the screen 122 in itself will not meet filterspecifications. It is too thin, not strong enough, it has too littlecapacity to efiecti'vely carry out the job of filtration.

Referring specifically to FIGS. 16-22, there is ill'ustrated a machinefor spirally rolling up the mat-screen component 122- 123 of FIGURE 14so as to lay up a plurality of turns of strip 123 in a uniform manneronto the screen 122. The inner screen 122 is mounted onto a suitablecylindrical mandrel support 124. Suitable end caps 125 and 126 areprovided at'the ends of the mandrel for holding the inner screenproperly positioned. The end cap 125 has a shaft 127 integral therewithby which it can be rotated. The end caps 125 and 126 have flanges 128which hold the screen cylinder 122 in position.

When the inner screen 122 with its attached metal fibril strip 123 hasbeen properly positioned on the mandrel 124 the mandrel and screen areplaced in a winding machine illustrated generally at 130, FIGURES 16,17, 20 and 21. This machine includes a main frame 131 having ahorizontal table 132, and a pair of spaced apart side plates 133, 133mounted thereon. A pair of cylindrical steel rollers 134 and 135 arerotatably mounted in suitable bearings 136 on side plates 133, 133 andextend between the two side plates. The centers of rotation of therollers 134 and 135 are fixed and so positioned that the inner screen122 with its mandrel 124 will ride upon the outer surfaces of therollers when the component 122-124-123 is placed between these rollersas shown in FIGURES 17, 20 and 21.

A pair of upright supports 140, 140 are mounted on the side plates 133,133` and extend upwardly therefrom. A pair of outwardly extending,parallel, spaced apart arms 141, 141 (see FIGURES 16 and 17) aredrivably mounted onto a shaft 142 which in turn is rotatably mounted insuitable bearings 143, 143 on the uprights 140. The shaft 142 extendsbetween the upright supports 140. A pressure roller 144 is rotatablymounted on suitable bearings 145 in a position between the outer ends ofthe arms 141, 141 and with the aXis of roller 144 parallel to the axesof rollers 134 and 135. The roller 144 is above the rollers 134 and 135,as can be seen in FIG. 17. A crank arm 146 is also pinned to shaft 142by pin 147. The control arm 146 extends rearwardly from the main frame131.

.A fluid actuated cylinder assembly 150 has its base pivotally attachedat 152 on lower bracket 151 on frame 131. A double acting piston incylinder 150 has piston rod 153 pivotally attached at 154 to the outerend of crank arm 146. The double-action cylinder is controlled byfiuidpressure through hoses 155 and 156 which extend back through position(Up-Otf-Down) control valve 157 so that the rod 153 can be extended orretracted under pressure.

The fluid supply is air and a suitable pressure regulator 16.0 islocated in a supply line 16-1 from a source 162. See FIGURE 16. Theregulator 160 is utilized for maintaining a uniform (but adjustable)pressure at the control valve 157 so that a known pressure can beintroduced into cylinder 150 so as to exert a known force on the rod 153for exerting a known force on the pressure roller 144.

When the winding machine 130` isv empty, the valve 157 is set so thatthe rod 153 is retracted and the arms 141, 141 are in the 'open positionas shown in dotted lines at 163 in FIG. 17. The roller 144 is thus rasedabove rollers 134 and 135. The inner screen 122 on its mandrel 124 withthe end caps and 126 in place is then placed on top of the rollers 134and and between the rollers with strip 123 extending forwardly fromunder the mandrel 124 and then hanging freely down over and in front oflower front roller 134. Since rollers 134 and 135 are spaced slightlyapart, the screen 122 will rest on top of both these rollers. The shaft127 on mandrel 124 has a suitable drive pin 166 mounted therein and thisdrive pin is adapted to fit into a slot 167 on the drive portion of afiexible coupling 168. The flexible coupling in turn is mounted onto ashaft 169 which is telescopically splined on coupling 170 which in turnis drivably mounted onto the output shaft 171 of a gear speed reducer172. A spring 175 is provided for urging the two couplings 170 and 168apart so that the groove 167 always engages the pin 166. The speedreducer 172 is driven by an adjustable speed electric motor 176 which ismounted on the reducer. When the motor 176 is energized the output shaft171 of the speed reducer will rotate and drive couplings 170-168 and theshaft 127, thereby turning the mandrel 124 and screen 122 thereon. Thiscauses the annealed strip of the fibril metal mat material 123 to berolled onto the inner screen 122, since the mat is tack welded to thescreen. Before the rolling-in of the strip 123 is'beg'un, valve 157 isoperated, and the air pressure is adjusted at 160 so as to force roller144 with a predetermined pressure down upon the inner screen 123, asshown in FIG. 17. Motor 176 is then started and the mandrel 124 andscreen 123 are thus rotated in direction as indicated by arrow 177;FIGURES 21-22. The strip of mat 123 will then start to wind up tightlyaround the screen 122 as shown in FIG. 20.

It will be observed that the strip of mat 123 will fit tghtly againstthe screen because the line of contact between the rollers 134, 135 and144 and the screen will be under a substantial and steady pressure.Therefore as the mat 123 is drawn in and wound on screen 122, forexample as the first revolution as shown in FIG. 20, the actualline-areas of contact between the pressure roller 144 and rollers 134and 135 with the mat will extend as three line-like areas `where each ofthe rollers contact the mat strip 123, one such area (between roller 144and the mat strip) being indicated at 178.

There are similar areas of contact where rollers 134 and 135 contact themat strip 123. It should be noted that the pressure on rollers 134 and135 together will support the load from the pressure roller 144 andtherefore the actual pressure on the metal fibril compact or mat will begreatest right directly beneath the pressure roller 144 in the area 178but all rollers contribute to the pressure compaction of each layer ofthe mat-strip 123.

As the mandrel continues to rotate, additional layers of the mat-strip123 will be laid on, each succeeding layer tightening down upon thelayers below. There is no tension on strip 123 as it is wound in.

The rolling-in of the mat-strip 123 is shown completed in FIGURE 21. Itwill be noted that the areas of contact of roller 144 and of rollers 134and 135 with the outermost layer of the rolled up mat-strip 123 haveincreased in area. This is due to the fact that there is a greaterradial depth of material into which the rollers can compress. The amountof pressure exerted by cylinder 150 can if desired, be caused toincrease as the winding approaches completion.

The end of the mat-strip 123 will be rolled until it actually makes asmooth overlap joint with the underlying turn of the strip. This ispossible because the strip 123 is quite thin and the metal fibrils areresilient and somewhat movable and will compress and shift as the

